1. Field of the Invention
The present invention relates to an improved device or mechanism for holding an optical element such as a lens, reflection mirror or prism in a lens barrel, frame or the like, as well as a method for manufacturing such a device or mechanism.
2. Description of the Prior Art
Heretofore, there have been various arrangements for holding an optical element such as a lens or a reflection mirror. Several examples thereof are shown in FIG. 1 through FIG. 4 of the drawings in each of which a lens L is held by a lens barrel 1 made of a synthetic resin or metal material.
FIG. 1 shows an arrangement in which a washer 3 has a male thread 3a formed on its outer circumference. A female thread meshing with the male thread 3a is formed on the lens barrel 1 to have the washer 3 retain and hold a lens L against the lens barrel 1. In this arrangement, since the thread has to be formed on the inner circumference of the lens barrel 1, if the lens barrel is made of a synthetic resin, the shape of the die for molding the lens barrel 1 is complicated, thereby increasing the cost of the device. Although the thread may be formed by machining after the molding of the lens barrel 1, this also increases the manufacturing cost, as well as resulting in the disadvantage that chips are liable to be produced upon screwing the threaded washer 3 into the lens barrel 1. Further, since the lens L is retained by the force of screwing the threaded washer 3, if a large force is used for ensuring a tight mounting, distortions may result particularly in the case of a thin lens. While on the other hand, if the screwing force is decreased, looseness may possibly result to render the holding effect unstable. In the case where the lens barrel 1 is made of metal, it also requires the step of forming the thread on the lens barrel 1 by machining, resulting in an increased cost as well.
FIG. 2 shows an arrangement in which a lens L is fixed by adhesives 4. In this case, although the lens distortions are less, since a limit is imposed on the bonding strength of the adhesives 4, it is not suitable for the holding of a heavy lens. Next, since it takes much time for the hardening of the adhesives 4, the assembling procedure is time-consuming. Further, the surface of the lens L tends to be clouded by gases such as any solvent generated from the adhesive 4. In addition, since it is difficult to uniformly coat the adhesive, the appearance is liable to be worsened.
FIG. 3 shows an arrangement using a spring washer 5 having a radial resiliency. A gap narrowing radially outwardly is formed between a lens barrel 1 and a lens L. The spring washer 5 is fitted tightly into the gap and urged by its resiliency against both the lens barrel 1 and the lens L to thereby hold the lens L. In this case, however, since the spring washer 5 intensely pressures both the lens barrel 1 and the lens L, distortions may be caused in both of the members. If the lens barrel 1 is distorted, focusing or similar operations cannot be conducted smoothly. Further, since the spring washer 5 is fitted into the gap in the condition of being resiliently deformed it may abut against and injure the lens L.
FIG. 4 shows an arrangement of fixing a lens L by heat caulking, in which a lens barrel 1 is formed with a flange 1b, which is heated and then deformed by a roller or spatula to thereby hold the lens L. In this case, since clearance for a roller R is necessary at a position in the lens barrel 1 outwardly from the outer circumference of the lens L as shown in FIG. 4 (b), the radial size of the lens barrel 1 must be increased as compared with the diameter of the lens. Particularly, in a case where the radius of curvature at the surface of the lens L is small or the lens L is located deeply within the lens barrel 1 as shown in FIG. 4(c), a large clearance, nearly the the diameter of the roller R, is necessary since the axis of the roller has to be placed almost in parallel with the optical axis, which neccessitates that the size of the lens barrel 1 be larger. Furthermore, since the flange 1b is successively pressed by the roller, even a slight error in the positioning of the roller will render the flange enforcing force non-uniform and cause distortions in the lens L.
As described above, conventional mechanisms and methods for holding a lens or other optical element employed so far have merits and demerits respectively, and no suitable arrangement has yet been attained.